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The elimination of H2 in the photodissociation of mono- and di-chloroethylenes was studied with a pump-and-probe technique. A 193 nm excimer laser was used to photodissociate the parent molecules, and a tunable dye laser was used to probe the H2 fragment by 2+1 resonance-enhanced multiphoton ionization (REMPI). The nascent rotational state distributions of H2(X 1Σ+g,v″=0–4) were extracted from the REMPI spectra, and were found to have Boltzmann-type distributions. The maximum and average translational energies for some of the rovibrational levels of H2 were measured using magic angle Doppler spectroscopy. The translational energy of the fragments plus the internal energy of H2 was found to exceed the available energy for a three-center elimination mechanism. It is concluded that a migration mechanism plays a significant role in H2 elimination. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Velocity-aligned Doppler spectroscopy was used to measure the speed distribution functions of HCl(v″=0–2,J″) produced in the 193 nm photodissociation of vinyl chloride. A mechanism which is consistent with our present data as well with our earlier work is three center elimination of HCl followed by concerted but nonsynchronous isomerization of the vinylidene fragment, with some of the isomerization energy converted to kinetic energy of the recoiling fragments. In order to explain the vibrational dependence of the translational and rotational energy distributions, the mechanism is assumed to be vibrationally adiabatic. In addition, magic angle Doppler spectroscopy was used to measure the speed distribution functions of Cl atoms produced in the photodissociation of vinyl chloride and the three dichloroethylene isomers. Bimodal energy distributions were observed for both spin–orbit states, with the Cl(2P1/2) fragment having more kinetic energy than Cl(2P3/2). The data are consistent with competitive reaction on two potential energy surfaces. Adiabatic correlation, with some scrambling in the asymptotic region, provide a qualitative explanation of the spin–orbit branching ratios. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]